Siloxane bischloroformates

ABSTRACT

Siloxane bischloroformates are prepared in a continuous process by phosgenating siloxane bisphenols in a flow reactor using a substantial excess of phosgene and sodium hydroxide. While very high levels (&gt;95%) of conversion of the siloxane bisphenol to the corresponding siloxane bischloroformate are achieved using a flow reactor according to the method of the invention, only more modest conversion (˜90%) of the siloxane bisphenol to the corresponding siloxane bischloroformate is attained when analogous batch processes are employed. The process holds promise for use in the manufacture of silicone-containing copolycarbonates which requires high purity siloxane bischloroformate intermediates.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method for the preparation ofsiloxane-containing bischloroformates. More particularly the methodrelates to a continuous method for the preparation ofsiloxane-containing bischloroformates in a flow reactor.

[0002] Silicone-containing copolycarbonates-are prized for their uniquecombination of ductility, toughness, and flame retardancy. Siliconecopolycarbonates are typically prepared by reaction of a mixture of asiloxane-containing bisphenol and a bisphenol such as bisphenol A underinterfacial conditions with phosgene and an aqueous acid acceptor suchas sodium hydroxide in water. Alternatively, silicone copolycarbonatesmay be prepared by reaction of a chloroformate-terminated polycarbonateoligomer with a siloxane-containing bisphenol. Typically, the reactionbetween the chloroformate-terminated polycarbonate oligomer and thesiloxane-containing bisphenol is carried out under interfacialconditions similar to those employed when a bisphenol and asiloxane-containing bisphenol are copolymerized directly with phosgene.Such approaches to silicone-containing copolycarbonates are illustratedin Japanese Patent Application JP 9265663, European Patent ApplicationEP 500131, U.S. Pat. No. 5,530,083, U.S. Pat. No. 5,502,134, andcopending U.S. patent application Ser. No. 09/613,040.

[0003] Siloxane-containing bischloroformates are potentially attractivechemical intermediates for the preparation of silicone-containingmaterials, including silicone-containing copolycarbonates in which thesilicone-containing monomer is incorporated into the polymer as anelectrophilic species. As such, improved methods for the preparation ofsiloxane-containing bischloroformates represent attractive goals. Thepresent invention provides a simple, continuous, high yield method forthe preparation of high purity siloxane-containing bischloroformateswhich is superior to known methods of bischloroformate preparation.

BRIEF SUMMARY OF THE INVENTION

[0004] In one aspect, the present invention provides a continuous methodfor the preparation of bischloroformates of siloxane bisphenols, saidmethod comprising introducing into a flow reactor at least one siloxanebisphenol, at least one alkali metal hydroxide or alkaline earth metalhydroxide, and phosgene, said phosgene being introduced at a rate suchthat the ratio of phosgene to siloxane bisphenol OH groups is in a rangebetween about 2.5 and about 6 moles of phosgene per mole of siloxanebisphenol OH group, said alkali metal hydroxide or alkaline earth metalhydroxide being introduced as an aqueous solution, said aqueous solutionhaving a concentration of at least about 5 percent by weight metalhydroxide, said metal hydroxide being introduced at a rate such that themolar ratio of metal hydroxide to phosgene is in a range between about3.5 and about 6.

[0005] In another aspect, the present invention relates to the highpurity siloxane bischloroformates which may be produced by the method ofthe present invention.

BRIEF SUMMARY OF THE DRAWING

[0006]FIG. 1 illustrates a tubular reactor system suitable for use inthe production of bischloroformates of siloxane bisphenols using themethod of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention may be understood more readily by referenceto the following detailed description of preferred embodiments of theinvention and the examples included herein. In this specification and inthe claims which follow, reference will be made to a number of termswhich shall be defined to have the following meanings.

[0008] The singular forms “a”, “an” and “the” include plural referentsunless the context clearly dictates otherwise.

[0009] “Optional” or “optionally” means that the subsequently describedevent or circumstance may or may not occur, and that the descriptionincludes instances where the event occurs and instances where it doesnot.

[0010] “BPA” is herein defined as bisphenol A and is also known as2,2-bis(4-hydroxyphenyl)propane, 4,4′-isopropylidenediphenol andp,p-BPA.

[0011] As used herein, the term “bisphenol A polycarbonate” refers to apolycarbonate in which essentially all of the repeat units comprise abisphenol A residue.

[0012] As used herein, the terms “siloxane-containing bischloroformates”and the term “siloxane bischloroformates” are used interchangeably andrefer broadly to any bischloroformate comprising one or more siloxaneunits. Siloxane bischloroformates comprise as a subgroupbischloroformates of siloxane bisphenols.

[0013] As used herein, the term “bischloroformates of siloxanebisphenols” refers to bischloroformates prepared fromsiloxane-containing bisphenols or their equivalents. The disodium saltof a siloxane bisphenol is an example of a species which would functionas the equivalent of a siloxane bisphenol.

[0014] As used herein, the terms “siloxane-containing bisphenol” and“siloxane bisphenol” are interchangeable and have the same meaning.Siloxane bisphenols are dihydroxy aromatic compounds incorporating oneor more siloxane repeat units. Typically, the siloxane bisphenols usedto prepare the siloxane bischloroformates are isomeric mixtures, saidisomeric mixtures arising in a double hydrosilylation reaction which istypically a synthetic step in the preparation of siloxane bisphenols.Typically, these isomeric mixtures comprise a single major isomer. Itwill be understood by those skilled in the art, however, that thestructure II given for the eugenol siloxane bisphenol used in theExamples and Comparative Examples is idealized in that it representsonly the major isomer present in an isomeric mixture. Similarly, each ofstructures III-IX represents an idealized structure meant to encompassinstances in which said structures represent only a major isomer presentin an isomeric mixture of siloxane bisphenols or siloxanebischloroformates. The description above should not be construed,however, as limiting the present invention to the use of isomericmixtures of siloxane bisphenols. The use of siloxane bisphenols whichare essentially single isomers falls well within the ambit of theinstant invention.

[0015] As used herein, the term “d-50 eugenol siloxane bisphenol”indicates a eugenol siloxane bisphenol having idealized structure IIwherein the average value of the integer p is about 50. For conveniencesake the term “d-50 eugenol siloxane bisphenol” is abbreviated EuSiD50.For convenience the mixture of isomeric d-50 eugenol siloxane bisphenolsII and X used in the Examples and Comparative Examples of the instantinvention has been represented as a single structure II, the structureof the major isomer present in said mixture, wherein p has an averagevalue of about 50.

[0016] The method of the present invention relates to a method for thecontinuous preparation of bischloroformates of siloxane bisphenols. Bycontinuous, it is meant that reactants are introduced into a suitablereactor system while products are simultaneously removed from thesystem. In the present invention at least one siloxane bisphenol,phosgene, and at least one alkali metal hydroxide or alkaline earthmetal hydroxide are introduced into a flow reactor. The reactants passthrough the flow reactor forming product bischloroformate during thepassage from the point, or points, at which the reactants are introducedand the point at which an effluent stream containing product emergesfrom the reactor. It has been discovered that product yields arestrongly and unexpectedly dependent upon reaction parameters such as therelative amounts of siloxane bisphenol, metal hydroxide, and phosgene,even when a substantial excess of phosgene or metal hydroxide ispresent. Additionally, it has been found that under similar conditionsoperation of the process in a continuous mode provides unexpectedly highyields relative to analogous batch processes.

[0017] In the practice of the present invention at least one siloxanebisphenol, phosgene, and at least one alkali metal hydroxide or alkalineearth metal hydroxide are introduced into a flow reactor. The flowreactor is not particularly limited and may be any reactor system whichprovides for the “upstream” introduction of the reactants and the“downstream” removal of product bischloroformate. Suitable flow reactorsystems include tubular reactors, continuous stirred tank reactors, loopreactors, column reactors, and combinations thereof. The flow reactormay comprise a series of flow reactor components, as for example, aseries of continuous stirred tank reactors arrayed such that theeffluent from a first continuous stirred tank reactor provides the inputfor a second continuous stirred tank reactor and so forth. Combinationsof the various flow reactor components are illustrated by a first columnreactor coupled to a downstream continuous stirred tank reactor wherethe output of the column reactor represents the feed to the continuousstirred tank reactor. Additionally, the flow reactor used according tothe method of the present invention may comprise flow reactor componentsarrayed in a parallel or network fashion, for example, as where thereactants are introduced into a parallel array of two or more tubularreactors the effluent of each of which is introduced into a singlecontinuous stirred tank reactor. In one embodiment of the presentinvention the flow reactor comprises a series of tubular reactors. In analternate embodiment the flow reactor comprises a series of continuousstirred tank reactors. The reactants may be introduced into the flowreactor system through one or more feed inlets attached to the flowreactor system. Typically, it is preferred that the reactants beintroduced into the flow reactor through at least three feed inlets, forexample where a solution of the siloxane bisphenol in an organic solventsuch as methylene chloride, aqueous alkali metal hydroxide, and phosgeneare introduced through separate feed inlets at or near the upstream endof a tubular reactor. Alternative arrangements wherein one or more ofthe reactants is introduced through multiple feed inlets at variouspoints along the flow reactor are also possible. Typically, the relativeamounts of the reactants present in the flow reactor are controlled bythe rate at which they are introduced. For example, a reactant can beintroduced into the flow reactor through pumps calibrated to deliver aparticular number of moles of said reactant per unit time.

[0018] The present invention employs phosgene (COCl₂) to convertsiloxane bisphenol OH groups into the corresponding chloroformategroups. It has been discovered that the amount of phosgene employedstrongly influences product yield. Phosgene is preferably used in anamount corresponding to between about 2.5 and about 6, even morepreferably between about 3.5 and about 5.5 moles of phosgene per mole ofsiloxane bisphenol OH group. Expressed in terms of moles of phosgene permole of siloxane bisphenol employed, it is preferable to use betweenabout 5 and about 12, and even more preferable between about 7 and about11 moles of phosgene per mole of siloxane bisphenol.

[0019] The alkali metal hydroxide or alkaline earth metal hydroxide, orcombination thereof is employed as an aqueous solution used in an amountpreferably corresponding to between about 3.5 and about 6, and even morepreferably between about 4 and about 5 moles of metal hydroxide per moleof phosgene employed. The concentration of the aqueous metal hydroxidesolution employed is preferably between about 5 and about 25, and evenmore preferably between about 17 and about 25 percent by weight metalhydroxide. In one embodiment of the present invention the concentrationof the metal hydroxide solution is at least about 5 percent by weight.Of course, more concentrated solutions of metal hydroxide may be used,as long as they are supplemented with water such that the net metalhydroxide concentration in aqueous solution is about 25% by weight orless.

[0020] The siloxane bisphenol is typically introduced into the flowreactor as a solution in a solvent. Typically the solvent is methylenechloride but can be any solvent suitable for use under interfacialreaction conditions. Typically halogenated solvents such as methylenechloride, chloroform, and 1,2-dichloroethane are preferred but othernon-halogenated solvents such as toluene or ethyl acetate may also beused. Typically the concentration of the siloxane bisphenol in thesolvent is in a range between about 5 and about 95, preferably betweenabout 10 and about 30 percent by weight siloxane bisphenol. As noted,the siloxane bisphenol employed may be a single chemical species or amixture of chemical species as is typical in siloxane bisphenols whichtypically comprise a distribution of bisphenols possessing siloxanesubunits of varying chain lengths. Alternatively, the siloxane bisphenolmay be introduced as an oil, without solvent.

[0021] In one embodiment of the present invention the siloxane bisphenolemployed comprises structure I

[0022] wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylenegroup optionally substituted by one or more C₁-C₁₀ alkyl or aryl groups,an oxygen atom, an oxyalkyleneoxy moiety

—O—(CH₂)_(t)—O—,

[0023] or an oxyalkylene moiety

—O—(CH₂)_(t)—,

[0024] where t is an integer from 2-20;

[0025] R² and R³ are each independently at each occurrence halogen,C₁-C₆ alkoxy, C₁-C₆ alkyl, or C₆-C₁₀ aryl;

[0026] z and q are independently integers from 0-4;

[0027] R⁴, R⁵, R⁶ and R⁷ are each independently at each occurrence C₁-C₆alkyl aryl, C₂-C₆ alkenyl, cyano, trifluoropropyl, or styrenyl; and

[0028] p is an integer from 1 to about 100.

[0029] Representative examples of siloxane bisphenols I include, but arenot limited to eugenol siloxane bisphenol II and other siloxanebisphenols, for example

[0030] structures III-VII shown below in which p is an integer from 1 toabout 100.

[0031] The representative siloxane bisphenols; eugenol siloxanebisphenol II, 4-allyl-2-methylphenol siloxane bisphenol III,4-allylphenol siloxane bisphenol IV, 2-allylphenol siloxane bisphenol V,4-allyloxyphenol siloxane bisphenol VI, and 4-vinylphenol siloxanebisphenol VII are named after the aliphatically unsaturated phenols fromwhich they are prepared. Thus, the name eugenol siloxane bisphenoldenotes a siloxane bisphenol prepared from eugenol(4-allyl-2-methoxyphenol). Similarly the name 4-allyl-2-methylphenolsiloxane bisphenol indicates the siloxane bisphenol prepared from4-allyl-2-methylphenol. The other names given follow the same namingpattern.

[0032] Siloxane bisphenols may be prepared by hydrosilylation of analiphatically unsaturated phenol with a siloxane dihydride in thepresence of a platinum catalyst. This process is illustrated below foreugenol siloxane bisphenol II.

[0033] In one embodiment of the present invention employing eugenolsiloxane bisphenol having structure II as a reactant, p is an integerbetween about 20 and about 100. In an alternate embodiment eugenolsiloxane bisphenol II has a value of p of about 50 said eugenol siloxanebisphenol being represented by the abbreviation EuSiD50. Those skilledin the art will understand that the values given for p in structuresI-VIII represent average values and that, for example, eugenol siloxanebisphenol having a value of p of 50 represents a mixture of siloxanebisphenol homologues having an average value of p of about 50.

[0034] Typically the reactants, siloxane bisphenol, aqueous metalhydroxide, and phosgene are introduced at one or more upstream positionsalong the flow reactor. As mentioned, the reactants pass through theflow reactor forming product bischloroformate during the passage fromthe point at which the reactants are introduced and the point at whichan effluent stream containing product emerges from the reactor. The timerequired for a reactant to travel from the point at which it isintroduced to the point at which either it or a product derived from itemerges from the flow reactor is referred to as the residence time forthe reactant. Typically, residence times for each reactant is in a rangebetween about 5 and about 800 seconds, preferably between about 10 andabout 500 seconds. Those skilled in the art will understand however thatthe most preferred residence time will depend upon the structure of thestarting siloxane bisphenol, the type of flow reactor employed and thelike, and that the most preferred residence time may be determined bystraightforward and limited experimentation.

[0035] In one embodiment the present invention provides a method for thepreparation of eugenol bischloroformate VIII

[0036] wherein p is an integer from 1 to about 100, said methodcomprising introducing into a flow reactor a eugenol siloxane bisphenolII

[0037] wherein p is an integer between 1 and about 100, as a solution inmethylene chloride comprising from about 5 to about 50 weight percenteugenol siloxane bisphenol, an aqueous solution of sodium hydroxide, andphosgene, said phosgene being introduced at a rate such that the ratioof phosgene to eugenol siloxane bisphenol OH groups is in a rangebetween about 2.5 and about 6 moles of phosgene per mole of eugenolsiloxane bisphenol OH group, said aqueous solution of sodium hydroxidehaving a concentration of at least about 5 percent by weight sodiumhydroxide, said aqueous solution of sodium hydroxide being introduced ata rate such that the molar ratio of metal hydroxide to phosgene is in arange between about 3.5 and about 6.

[0038] One embodiment of the present invention is a siloxanebischloroformate produced by the method described herein. Thus, in oneaspect the present invention is a siloxane bischloroformate produced bythe method of the present invention said siloxane bischloroformatecomprising structure IX

[0039] wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylenegroup optionally substituted by one or more C₁-C₁₀ alkyl or aryl groups,an oxygen atom, an oxyalkyleneoxy moiety

—O—(CH₂)_(t)—O—,

[0040] or an oxyalkylene moiety

—O—(CH₂)_(t)—,

[0041] where t is an integer from 2-20;

[0042] R² and R³ are each independently at each occurrence, halogen,C₁-C₆ alkoxy, C₁-C₆ alkyl, or C₆-C₁₀ aryl;

[0043] z and q are independently integers from 0-4;

[0044] R⁴, R⁵, R⁶ and R⁷ are each independently at each occurrence C₁-C₆alkyl, aryl, C₂-C₆ alkenyl, cyano, trifluoropropyl, or styrenyl; and

[0045] p is an integer from 1 to about 100.

[0046] In a further embodiment, the present invention affords highpurity bischloroformates having low levels of residual hydroxyendgroups. Thus when siloxane bisphenols having structure I areconverted using the method of the present invention to the correspondingsiloxane bischloroformates having structure IX, the productbischloroformate IX contains less than 10 percent, preferably less than5 percent and even more preferably less than 1 percent residual hydroxyendgroups. The term “residual hydroxy endgroups” refers to those hydroxygroups present in the starting siloxane bisphenol which are notconverted to the corresponding chloroformate groups in the productbischloroformate. During the course of the present invention it wasdiscovered that the principal impurities present in the product siloxanebischloroformate are the starting siloxane bisphenol andbischloroformate half product as determined by ¹H-NMR spectroscopy.Comparative Example 1 illustrates the high levels of residual hydroxyendgroups present in product siloxane bischloroformate prepared usingconventional batch reaction conditions which have been used to prepareother types of chloroformates.

[0047] In a further embodiment the present invention is a siloxanebischloroformate comprising structure VIII wherein p is an integerbetween 1 and about 100, said siloxane bischloroformate comprising fewerthan 10 percent hydroxy endgroups, said siloxane bischloroformatecomprising less than 0.5 percent carbonate groups.

EXAMPLES

[0048] The following examples are set forth to provide those of ordinaryskill in the art with a detailed description of how the methods claimedherein are carried out and evaluated, and are not intended to limit thescope of what the inventors regard as their invention. Unless indicatedotherwise, parts are by weight and temperature is in ° C. Percentconversion of eugenol siloxane bisphenol OH groups to the correspondingchloroformate groups was determined by proton NMR spectroscopy (¹

[0049] The starting siloxane bisphenol, d-50 eugenol siloxane bisphenol(EuSiD50), used in the preparation of siloxane bischloroformates wasitself prepared by hydrosilylation of approximately two equivalents ofeugenol with approximately one equivalent of the d-50 siloxanedihydride, HSiMe₂(OSiMe₂)₅₀H, under known hydrosilylation conditions,for example those taught in copending U.S. application Ser. No.09/613,040. The product eugenol siloxane bisphenol was shown by ¹H-NMRto be a 95:5 mixture of isomeric siloxane bisphenols, said isomericsiloxane bisphenols having structures II and X respectively,

[0050] wherein p is a range of integers having an average value of about50.

[0051] As mentioned, isomeric mixtures such as the mixture of siloxanebisphenols having structures II and X are idealized as having thestructure of the major isomer II for reasons of convenience. Thoseskilled in the art will understand that the olefin hydrosilylationchemistry employed to produce bisphenol siloxanes will almost invariablyproduce the product siloxane bisphenols as a mixture of isomers, saidmixture of isomers frequently being inseparable and yet useful inmaterials synthesis. Those skilled in the art will likewise understandthat the conversion of a mixture of isomeric siloxane bisphenols to thecorresponding bischloroformates will necessarily produce an isomericmixture of siloxane bischloroformates. As in the case of the siloxanebisphenols, the structures of said siloxane bischloroformates areidealized herein as having the structure of the major siloxanebischloroformate isomeric component. Thus, the eugenol siloxanebischloroformate prepared in the Examples and Comparative Examplesherein was an approximately 95:5 mixture of the siloxanebischloroformates corresponding to siloxane bisphenols II and X. Forconvenience in describing the practice and attributes of the instantinvention, isomeric mixtures of eugenol siloxane bischloroformates aretreated as having idealized structure VIII.

[0052] Three feed solutions, a 20 weight percent solution of d-50eugenol siloxane bisphenol (EuSiD50) in methylene chloride, NaOH inwater, and phosgene were introduced into a tubular flow reactor in theamounts and feed rates indicated. The tubular flow reactor employed isshown in FIG. 1. Each feed solution was delivered independently to thereactor. The d-50 eugenol siloxane bisphenol in methylene chloride(CH₂Cl₂) solution was pre-cooled in coil immersed in an ice water bath.The discharge end of the reactor was vented to a scrubber at atmosphericpressure. The pressure at the feed side of the reactor was 3-5 psig. Thetubular flow reactor comprised a series of KO-FLO® static mixersconfigured as follows: one Type A tubular reactor section followed bysix Type B tubular reactor sections. The Type A tubular reactor sectioncomprised six static mixers, each of said mixers being 7 inches inlength and having an outer diameter of ¼ of an inch. Each of the Type Btubular reactor sections comprised three static mixers; a first staticmixer (11 inches in length, ¼ inch outer diameter), a second staticmixer (16 inches in length, ⅜ inch outer diameter), and a third staticmixer (16 inches in length, ½ inch outer diameter). The total reactorvolume was about 252 milliliters (mL). The initial sections of thereactor were wrapped with woven fabric insulating material. Samplingpoints were located at several locations along the flow reactor and areindicated in FIG. 1 as “Point 1”-“Point 8”, “Point 12” and “Sample Point13”. Sample point 13 was located at the downstream end of the sixth TypeB tubular reactor section and corresponded to a reactor volume of about252 mL. Sample point 8 was located at the downstream edge of the firsttype B tubular reactor section (that tubular reactor section followingthe Type A reactor section) and corresponded to a reactor volume ofabout 57 mL. Sample point 7 was located at the downstream end of theType A tubular reactor section. Typical residence times are illustratedby Example 2 wherein the residence time was about 90 seconds at samplepoint 8 and about 400 seconds at sample point 13. In Examples 1-6 feedsolutions (1) and (3) were introduced at the following rates:

[0053] Feed (1): 7.6 gram/minute (gm/min)EuSiD50 (d-50 eugenol siloxane)30.4 gram/minute methylene chloride

[0054] Feed (3): 1.12 gram/minute COCl₂

[0055] The data in Table 1 demonstrate that using the method of thepresent invention greater than 95% conversion of eugenol siloxanebisphenol hydroxy groups to the corresponding bischloroformates can beachieved while avoiding carbonate byproduct formation. In Examples 1-6optimal performance was achieved when the molar ratio of sodiumhydroxide to eugenol siloxane bisphenol hydroxy groups was in a rangebetween about 9 and about 12 and the concentration of the aqueous sodiumhydroxide was about 17.5 percent by weight sodium hydroxide in water.TABLE 1 EUGENOL SILOXANE BISCHLOROFORMATE PREPARATION Moles Wt % NaOHFeed 2 % Conversion % Conversion Carbonate Example NaOH^(a) (Feed 2)^(b)rate^(c) at 8^(d) at 13^(e) level^(f) 1 6 17.5 5.18 82.8 <0.5% 2 9 17.57.77 94.4 95.3 <0.5% 3 12 17.5 10.36 96.3 96.5 <0.5% 4 6 12.5 5.18 72.8<0.5% 5 9 12.5 7.77 88.9 <0.5% 6 12 12.5 10.36 92.9 93.2 <0.5%

Comparative Example 1

[0056] A 500 mL Morton flask was charged with d-50 eugenol siloxanebisphenol (5.0 g, 0.12 mmol), methylene chloride (130 mL) and water (10mL). The pH was adjusted to and maintained at a pH of from about 0 toabout 5 with 25 wt % aqueous sodium hydroxide as phosgene (5.0 g, 50mmol) was added. Following phosgene addition the pH was raised to about10 to consume excess phosgene. Hydrochloric acid solution (1N HCL, 135mL) was added and the product bischloroformate solution was separated bycentrifugation. Proton NMR analysis showed only about 90% of the eugenolsiloxane bisphenol hydroxy groups had been converted to chloroformategroups. There was little or no carbonate coupled product.

Examples 7-24

[0057] The flow reactor used in Examples 7-24 was essentially identicalto that used in Examples 1-6 with the following modifications. The flowreactor was configured as shown in FIG. 1. A sample port was added tothe system at the downstream end of the first reactor section (Type Atubular reactor section) and a cooler was installed to provide coolingfor the aqueous caustic feed in selected experiments. Examples 17-22utilized the aqueous caustic cooler. In each of Examples 7-24 thesolution of eugenol siloxane bisphenol in methylene chloride (CH₂Cl₂)was chilled in an ice water bath prior to its introduction into the flowreactor solution cooler. Detailed Experimental conditions used inExamples 7-24 are given Table 2. Additional experimental data andresults for the conversion of starting eugenol siloxane bisphenol toproduct eugenol siloxane bischloroformate in Examples 7-24 are gatheredin Table 3. Feed rates employed in Examples 7-24 for eugenol siloxanebisphenol, methylene chloride and phosgene are given below. Feed 1:  7.6gram/minute EuSiD50 30.5 gram/minute CH₂Cl₂ Feed 2: COCl₂ (see tablesfor flow rates) Feed 3: Aqueous NaOH (see tables for flow rates)

[0058] TABLE 2 EUGENOL SILOXANE BISCHLOROFORMATE REACTION CONDITIONSResidence NaOH Point 6 Feed Time Residence COCl2 Soln NaOH Temp PressurePoint 7 Time Example gm/min gm/min ° C. ° C.^(a) psig (sec) Point 13(sec) 7 1.12 10.38 15.8 43.3 5 —  804^(b) 8 1.12 12.12 13.2 38.5 2 27379 9 1.50 16.17 14.9 41.1 3 25 349 10 1.12 15.16 14.5 35.5 2.5 25 35611 1.50 20.21 16.2 40.5 4 23 323 12 1.12 9.09 12.6 38.1 3 29 410 13 1.5012.12 12.2 42.5 4.2 27 384 14 1.12 11.37 11.9 34.9 2.0 28 390 15 1.5015.16 12.9 41.5 3.8 26 361 16 1.31 11.93 12.8 40.0 3 27 383 17 1.5015.16 8.5 30.5 3 26 361 18 1.69 17.05 8.8 33.1 3 25 347 19 1.87 18.945.8 31.4 3 24 335 20 1.50 12.63 6.7 34.3 3 27 383 21 1.69 14.21 6.2 36.53.8 26 371 22 1.87 15.79 7.2 39.3 4 26 360 23 1.87 15.79 11.4 40.2 5 26360 24 1.87 17.22 14.0 43.8 4.5 26 360

[0059] TABLE 3 EUGENOL SILOXANE BISCHLOROFORMATE PREPARATION Molar ratioCOCl₂/ Ex- Eugenol % Conversion to % Conversion to am- siloxane NaOH/ wt% Chloroformate Chloroformate ple OH COCl₂ ^(a) NaOH Sample Point 7Sample Point 13 7 3 4 17.5 — 97.7 8 3 4 15  84.7^(b) 91.3 9 4 4 15 93.097.1 10 3 5 15 85.8 91.7 11 4 5 15 97.6 98.5 12 3 4 20 88.4 96.6 13 4 420 98.0 98.5 14 3 5 20 91.3 95.7 15 4 5 20 99.0 99.0 16 3.5 4.5 17.597.1 97.1 17 4 5 20 85.5 97.6 18 4.5 5 20 87.3 98.0 19 5 5 20 88.1 99.520 4 5 24 84.4 98.0 21 4.5 5 24 85.1 99.0 22 5 5 24 94.8 99.5 23 5 5 24— >99.5 24 5 5 22 — >99.5

[0060] The data in Table 3 demonstrate that essentially completeconversion of eugenol siloxane bisphenol to eugenol siloxanebischloroformate is achievable using the method of the presentinvention. With the single exception of Example 11 in whichapproximately 1 percent of the eugenol siloxane bisphenol OH groups wereconverted to carbonate groups, no carbonate was detected by proton NMR.Thus, the method of the present invention is clearly superior to thebatch preparation of eugenol siloxane bischloroformate illustrated byComparative Example 1.

[0061] The invention has been described in detail with particularreference to preferred embodiments thereof, but it will be understood bythose skilled in the art that variations and modifications can beeffected within the spirit and scope of the invention.

What is claimed is:
 1. A continuous method for the preparation ofbischloroformates of siloxane bisphenols, said method comprisingintroducing into a flow reactor at least one siloxane bisphenol, atleast one alkali metal hydroxide or alkaline earth metal hydroxide, andphosgene, said phosgene being introduced at a rate such that the ratioof phosgene to siloxane bisphenol OH groups is in a range between about2.5 and about 6 moles of phosgene per mole of siloxane bisphenol OHgroup, said alkali metal hydroxide or alkaline earth metal hydroxidebeing introduced as an aqueous solution, said aqueous solution having aconcentration of at least about 5 percent by weight metal hydroxide,said metal hydroxide being introduced at a rate such that the molarratio of metal hydroxide to phosgene is in a range between about 3.5 andabout
 6. 2. A method according to claim 1 wherein said siloxanebisphenol comprises structure I

wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylene groupoptionally substituted by one or more C₁-C₁₀ alkyl or aryl groups, anoxygen atom, an oxyalkyleneoxy moiety —O—(CH₂)_(t)—O—, or an oxyalkylenemoiety —O—(CH₂)_(t)—, where t is an integer from 2-20; R² and R³are eachindependently at each occurrence halogen, C₁-C₆ alkoxy, C₁-C₆ alkyl, orC₆-C₁₀ aryl; z and q are independently integers from 0-4; R⁴, R⁵, R⁶ andR⁷ are each independently at each occurrence C₁-C₆ alkyl, aryl, C₂-C₆alkenyl, cyano, trifluoropropyl, or styrenyl; and p is an integer from 1to about
 100. 3. A method according to claim 2 wherein said siloxanebisphenol is a eugenol siloxane bisphenol having structure II

wherein p is an integer from 1 to about
 100. 4. A method according toclaim 3 wherein p is an integer from about 10 to about
 100. 5. A methodaccording to claim 2 wherein said siloxane bisphenol is selected fromthe group consisting of 4-allyl-2-methylphenol siloxane bisphenol III

2-allylphenol siloxane bisphenol V

and 4-vinylphenol siloxane bisphenol VII

wherein in structures III, V, and VII p is an integer from 1 to about100.
 6. A method according to claim 1 wherein said siloxane bisphenol isintroduced into said flow reactor as a solution in an organic solvent.7. A method according to claim 6 wherein said solution comprises ahalogenated solvent selected from the group consisting of methylenechloride, chloroform, and 1,2-dichloroethane.
 8. A method according toclaim 1, said method being further characterized as having a reactantresidence time, said residence time being in a range between about 5seconds and about 800 seconds.
 9. A siloxane bischloroformate producedby the method of claim
 1. 10. A siloxane bischloroformate comprisingstructure IX and comprising fewer than 10 percent hydroxy endgroups

wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylene groupoptionally substituted by one or more C₁-C₁₀ alkyl or aryl groups, anoxygen atom, an oxyalkyleneoxy moiety —O—(CH₂)_(t)—O—, or an oxyalkylenemoiety —O—(CH₂)_(t)—, where t is an integer from 2-20; R² and R³ areeach independently at each occurrence, halogen, C₁-C₆ alkoxy, C₁-C₆alkyl, or C₆-C₁₀ aryl; z and q are independently integers from 0-4; R⁴,R⁵, R⁶ and R⁷ are each independently at each occurrence C₁-C₆ alkyl,aryl, C₂-C₆ alkenyl, cyano, trifluoropropyl, or styrenyl; and p is aninteger from 1 to about
 100. 11. A continuous method for the preparationof eugenol siloxane bischloroformate VIII

wherein p is an integer from 1 to about 100, said method comprisingintroducing into a flow reactor a solution of eugenol siloxane bisphenolII

wherein p is an integer between 1 and about 100, said solutioncomprising methylene chloride, an aqueous solution of sodium hydroxide,and phosgene, said phosgene being introduced at a rate such that theratio of phosgene to eugenol siloxane bisphenol OH groups is in a rangebetween about 2.5 and about 6 moles of phosgene per mole of eugenolsiloxane bisphenol OH group, said aqueous solution of sodium hydroxidehaving a concentration of at least about 5 percent by weight sodiumhydroxide, said aqueous solution of sodium hydroxide being introduced ata rate such that the molar ratio of metal hydroxide to phosgene is in arange between about 3.5 and about
 6. 12. A method according to claim 11,said method being further characterized as having a reactant residencetime, said residence time being in a range between about 5 seconds andabout 800 seconds.
 13. A method according to claim 11 wherein saidsolution of eugenol siloxane bisphenol comprising methylene chloridecomprises about 20 percent by weight eugenol siloxane bisphenol II. 14.A method according to claim 11 wherein said aqueous solution of sodiumhydroxide comprises from about 15 to about 24 percent by weight sodiumhydroxide.
 15. A method according to claim 11 in which said flow reactoris selected from the group consisting of one or more tubular reactors,one or more continuous stirred tank reactors, one or more loop reactors,a column reactor, or a combination thereof.
 16. A method according toclaim 11 wherein said flow reactor comprises a series of tubularreactors.
 17. A method according to claim 11 wherein said flow reactorcomprises a series of continuous stirred tank reactors.
 18. A siloxanebischloroformate prepared by the method of claim
 11. 19. A siloxanebischloroformate comprising structure VIII

wherein p is an integer between 1 and about 100, said siloxanebischloroformate comprising fewer than 10 percent hydroxy endgroups.